Record the initial Map in the Store IC if it is not the same as the transitioned Map

src/ic.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1663 matching lines @@
     // copying COW arrays and silently ignoring some OOB stores into external
     // arrays, but for now use the generic.
     TRACE_GENERIC_IC(isolate(), "KeyedIC", "COW/OOB external array");
     return strict_mode == kStrictMode
         ? generic_stub_strict()
         : generic_stub();
   }
 
   State ic_state = target()->ic_state();
   Handle<Map> receiver_map(receiver->map(), isolate());
+  MapHandleList target_receiver_maps;
   if (ic_state == UNINITIALIZED || ic_state == PREMONOMORPHIC) {
     // Optimistically assume that ICs that haven't reached the MONOMORPHIC state
     // yet will do so and stay there.
     Handle<Map> monomorphic_map = ComputeTransitionedMap(receiver, store_mode);
     store_mode = GetNonTransitioningStoreMode(store_mode);
-    return isolate()->stub_cache()->ComputeKeyedStoreElement(
-        monomorphic_map, strict_mode, store_mode);
+    if (*monomorphic_map != *receiver_map) {
+      target_receiver_maps.Add(receiver_map);
+      target_receiver_maps.Add(monomorphic_map);
+      return isolate()->stub_cache()->ComputeStoreElementPolymorphic(
+          &target_receiver_maps, store_mode, strict_mode);
+    } else {
+      return isolate()->stub_cache()->ComputeKeyedStoreElement(
+          monomorphic_map, strict_mode, store_mode);
+    }
   }
 
-  MapHandleList target_receiver_maps;
   target()->FindAllMaps(&target_receiver_maps);
   if (target_receiver_maps.length() == 0) {
     // In the case that there is a non-map-specific IC is installed (e.g. keyed
     // stores into properties in dictionary mode), then there will be not
     // receiver maps in the target.
     return strict_mode == kStrictMode
         ? generic_stub_strict()
         : generic_stub();
   }
 
@@ skipping 1094 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal